The present invention relates to a dry method for the preparation of cationic galactomannans by means of reaction with alkylene epoxides in the presence of water in an alkaline medium.
Galactomannans are an important group of vegetable hydrocolloids which occur as reserve carbohydrates, analogous to starch, especially in the seed endosperm of many Leguminosae (legumes). However, only guaran (guar gum) and carubin (fine carob [Saint John's bread] flour) are of practical industrial significance. Guaran occurs in the endosperm of guar beans (Cyamopsis tetragonoloba L.), which belong to the order of Leguminosae, family Papilionaceae. Guar is an old cultivated plant which is cultivated today especially in India, Pakistan and Texas on a large scale.
Guaran contains 64% mannose and 36% galactose. The mannose structural elements linked in a beta-(1,4)-glycosidic bond form long, unbranched chains to which individual galactose molecules are attached in alpha-(1,6)-bonds. Both mannose as well as galactose are present in pyranose form. The average molecular weight of guaran is around 220000. Guaran is soluble in cold water.
Native and modified galactomannans based on fine guar flours and fine carob flours are used industrially today in many different areas, e.g. in the petroleum, textile, paper, food, pharmaceutical, cosmetic and explosives industries as well as in mining and in water treatment. The native galactomannans have been known for years in the manufacture of paper as a "wet end additive" for increasing paper strengths. As a result of modification, the properties of the products can be reinforced or products with completely new properties can be created.
In order to improve the natural affinity of galactomannans for cellulose and thus be able to achieve a better retention of the fine fibers, there is the possibility of cationizing galactomannans.
European Pat. No. A0 146 911 discloses a method in which 2,3-epoxypropyltrimethyl ammonium chloride is reacted in an alkaline, aqueous medium at 52.degree. C.
According to European Pat. No. A0 130 946, this reaction is likewise performed in an alkaline medium which, however, contains sodium tetraborate in addition and is partially neutralized by acetic acid before the addition of the cationizing reagent.
Great Britian Pat. No. 1,136,842 contains more precise data about products like those obtained in the reaction of 2,3-epoxypropyltrimethyl ammonium chloride with galactomannans in an alkaline, aqueous medium.
According to these publications, the cationized product must be dried, then ground and sieved before further usage.